Treatment of fluid pervious formations



Patented June 8, 1943 TREATMENT OF FLUID PERVIOUS FORMATION S John J. Grebe and Leonard C. Chamberlain, Midland, Mich., assig'nors to The Dow Chemical Company, Midland, Mich., a corporation of Michigan No Drawing. Application May 2, 1938,

, Serial No. 205,534

9 Claims.

The invention relates to the treatment of fluid pervious earth or rock formations. It more particularly concerns an improved method of bringing about the formation -*'of a sealing and consolidating deposit in the pores of an'earth or rock formation, especially those traversed or penetrated by the bore of a deep well, e. g. an oil or gas Well.

It has been proposed to treat earth formations by introducing thereinto a solution of an electrolyte which reacts with the natural brine or water in the formation or with a similar solution introduced thereinto to produce a precipitate in the pores and interstices of the formation to bring about sealing and consolidation. However, this method has the disadvantage that only a small proportion of the precipitable ions contained in the electrolyte solutions meet and unite to produce a precipitate in the formation, because the solutions do not readily mix in the earth formation but rather just meet each other at the boundary of each body of liquid. As a consequence only those precipitable ions contained in the boundry. surface of the two solutions unite to form a precipitate, while the major portion of precipitable ions contained in the solution never react to produce a precipitate .since they do not meet. Thus the production of an amount of precipitate that will effectively seal up the pores of a permeable formation is not often obtainable by use of the conventional method.

The principal object of the invention is to provide a method whereby the foregoing difficulties are substantially overcome and new and improved results as regards the plugging and sealing effect are obtained when solutions of electrolytes are introduced into an earth formation.

Another object is to provide a method of treating a brine or water bearing stratum penetrated by the bore of an oil or gas well to selectively shut off the infiltration of brine or water without substantially affecting the flow of oil or gas into the well.

Other objects and advantages will be apparent as the description of the invention proceeds.

According to our invention an aqueous solution of an electrolyte is introduced into the for- The effect of the electrolysis is to greatly accelerate the rate of diffusion of the ions so that they soon become mixed, thereby reacting and increasing the amount of deposit produced in the pores and interstices of the formation. As a result a more effective sealing and consolidating action is obtained.

It is first necessary to introduce the electrolyte solution or solutions to be subjected to the action In case the formation to be treated is located at a considerable depth beneath the surface of the earth so that perforated pipe or well points can not be made to readily penetrate the iormation. a well bore or series of well bores may be drilled in the conventional manner and the solution or solutions introduced into the formation thcrethrough. In treating water or brine formations already penetrated by a well, such as an oil well, to bring about sealing or consolidation of the formation, the injection of the solutions into the desired formation is made through the bore of the well. After the solutions have been located in the desired formation, an electric current is passed between electrodes located in the formation containing the solutions. The ions contained in the solutions are caused to migrate by the current and precipitate to form a rela tively impermeable seal in the formation.

In carrying out the method of the invention to prevent the infiltration of water from a source such as a river into an excavation, a short distance from the banks of the river, aseries of perforated pipes,well points, or the like are driven into the earth between the river and the excavation, preferably parallel to and, along the river bank. The injection pipes should be located at a distance of between about 5-25 feet apart so that the solutions readily permeate the porous portions of the formation between the injection pipes, and should extend at least along the en-' tire length of the face of the excavation. facing the river and to a depth below that at'which the infiltration is occurring. The solutions containing the ions which react to produce a, relatively insoluble precipitate may then be successively introduced into each separate injection pipe. After the solutions have been properly located in the formation to be treated, an electric current is passed between the injection pipes, which may serve as one series of electrodes, and copper rods or the like which serve as the other series of electrodes, driven into the earth a suitable distance from the injection pipes, say about 20-30 feet. The copper rods or the like may be located on either side of the injection pipes, that is either between the injection pipes and the river or between the injection pipes and the excavation. The injection pipes and the copper electrodes are connected to a source of direct current at from about to 100 volts or more. The current passing through the formation and through the solutions causes the ions contained therein to migrate so that the precipitable ions meet in the formation and form a substantially impermeable wall of precipitate at the point of meeting in the permeable formation between each row of electrodes. This wall of precipitate formed between the rows of electrodes, i. e. between the river bank and the excavation, then prevents infiltration of water. If desired, a double row of injection pipes may be located parallel to the excavation and one ,of the solutions introduced into one row of pipes while the other solution is introduced into the formation through the other row of pipes. Various other arrangements of injection pipes and electrodes may be employed to meet specific conditions, such as in sealing the formation surrounding any type of excavation, mine shafts, cellars, canals, or the like against the infiltration of fluids from the surrounding formation.

As amore specific embodiment of the invention, the infiltration of brine or water into an oil well, for example, may be shut oil in the following manner: An aqueous solution of an electrolyte is introduced into the well and pressure is applied slightly in excess of the bottom hole pressure to displace the solution of electrolyte from the bore hole. Since under the condition of slight excess of pressure, aqueous solutions enter brine formations in preference to oil or gas formations, danger of subsequently plugging the oil or gasformation is virtually eliminated. The aqueous solutions employed should contain ions capable of reacting with those of the natural waters in the formation to produce a precipitate.

If the earth formation does not contain a natural solution of an electrolyte, e. g. brine, another solution of an electrolyte may also be introduced while maintaining the specified pressure. The second solution of electrolyte should contain an ion which will unite with an ion contained in the solution first introduced to form a water insoluble precipitate when an electric current is passed through the solution. The second solution is allowed to penetrate the formation, forcing the first electrolyte solution back into the formation, enough being retained, in the bore hole, however, to cover the formation to be Plugged and to make a suitable contact with an electrode lowered into the well.

After the solutions are in place an electrode is lowered into the well on an insulated conducting cable until it is opposite the formation to be treated and immersed in the solution of electrolyte standing in the well bore. The solutions are then electrolyzed by passing an electric current through them from a source of potential, such as a generator, the circuit being completed through a ground electrode connected to one pole CJI of the generator. During electrolysis, pressure is maintained upon the solutions, if necessary, to prevent them from returning to the well bore. When the solutions are electrolyzed in the formation, they are caused to mix due to the resulting migration of the ions of the solutions. The migrating ions react together to produce a precipitate in situ and precipitation continues as long as the current is passed, until the solutions are exhausted. At the same time the strength of the current which fiows under a given applied voltage gradually declines and this decrease in current flow is an indication of the amount of precipitation and sealing which is being produced. In time'the pore spaces become completely sealed with the precipitate produced and the resistance to the passage of current approaches a maximum. thus indicating that the electrolysis may then be discontinued. Upon completing the electrolysis, the electrode is withdrawn from the bore and the residual solution in the well bore removed, as by bailing, before putting the well into production.

The amount of the solutions of electrolytes to be employed depends upon a number of virables, such as for example, the thickness and extent of the formation to be treated and its permeability. In the case of a well such as just described, the second solution, if used, may be forced into the formation a distance of from a few inches to several feet from the well bore. depending upon the distance from the well bore it it desired to bring about precipitation of the ma-- terial due to electrolytic action. As an example, we have found that good results-were obtained in a well having a brine bearing stratum about 10 feet thick by introducing about 1000 gallons of the solution containing about 10 per cent of the electrolyte.

The following are examples of solutions containing ions which we have found to be useful for the treatment of earth or rock formations according to the invention:

Example 1 Example 2 A sodium oxalate solution and a calcium chloride solution are introduced successively into a permeable formation not containing brine. and

, when electrolyzed therein form a substantially insoluble calcium oxalate precipitate.

Example 3 An aluminum chloride solution and a sodium carbonate solution are separately introduced into the formation, and when electrolyzed therein form a substantially insoluble aluminum hydroxide precipitate.

' Example 4 A sodium sulfate solution and a calcium chloride solution are separately introduced into the formation and when electrolyzed therein form a substantially insoluble calcium sulfate precipitate.

In many cases the formation to be treated may contain a brine, such as a calcium chloride solution, containing a suitable ion of a suitable concentration, making it unnecessary to add more than one electrolyte solution before electrolyzing, as in Example 1, for instance. These same electrolyte solutions can be used, however, in formations which do not contain calcium chloride or like brine by introducing such a brine into the formation.

The concentration of the electrolyte in the aqueous solution to be employed may vary greatly. In general, a suitable concentration is from 2-15 per cent by weight of the anhydrous electrolyte salt or soluble chemical which yields a suitable ion when dissolved in water. It is desirable to employ a concentration such that equivalent amounts of the precipitating ions are contained in the respective solutions used, in order to obtain the best efiiciency from the solutions.-

It is oftentimes desirable to have a high concentration of electrolyte around the electrodes, because otherwise the electrolytes surrounding the electrodes become depleted in ions during the electrolysis, thus increasing the potential which must be applied to cause the current to flow. This difficulty may be overcome by injecting an electrolyte having a relatively high concentration of ions around the electrodes so that material depletion of the solution does not occur readily, as by making additional injections of electrolyte around the electrodes and injection pipes used as electrodes as the electrolysis proceeds.

Sometimes it is advantageous to keep the solution of electrolyte introduced into the formation separated from the solution of electrolyte already present in the formation or introduced thereinto until deep penetration has been effected, in order that the partial precipitation which would ordinarily occur upon contact of the two solutions is delayed until they are subjected to electrolysis in the formation. The separation of the two solutions may be accomplished by introducing into the formation ahead of the solution containing the ion which will unite with and precpitate upon uniting with an ion present in the brine in the formation or introduced thereinto for the purpose, a solution containing ions which will not unite with the ions present in the other solution of the electrolyte to form a precipitate. For example, an aqueous solution of sodium chloride introduced into -the formation, between any two of the solutions of electrolytes mentioned above, or similar solutions, will effectively prevent their precipitation until they are electrolyzed. In general the order of introduction of the precipitating electrolytes into the formation is not important.

The voltage which should be applied to effect electrolysis of the solutions depends upon the conductivity of the earth in the more immediate vicinity of the electrolyte. As aforementioned, the voltage required can be materially reduced by the injection of electrolytes around the electrodes, especially as the electrolysis proceeds. A sufficient potential is applied to produce a current in the order of about 5-75 amperes per earth or rock to migrate away from its point of v For example, negative pre ipi introduction. table ions migrate away from the negative electrode toward the positive electrode and vice versa.

Examples of such negative ions are carbonate, sulfate, oxalate, sulfite, etc. as calcium, aluminum, etc., migrate away from the positive electrode.

The electrodes may be made from any suitable material, such as graphite, carbon, or metals such as iron or copper. When the treatment is being carried out in a deep well, such as an oil well, the ground connections may be made through metal rods or the like driven into the ground in the vicinity of the well, preferably in moist earth about half as far from the well head as the depth of the stratum to be treated. The well casing may be used as one of the electrodes.

By the foregoing method fluid permeable earth and rock and loose or unconsolidated formations can be rendered substantially fluid impermeable. The method has particular advantage in the treatment of oil or gas wells yielding water or brine from a stratum closely adjacent the one yielding oil or gas, because the comparatively highelectrical resistance of an oil or gas formation prevents the current from passing through it and consequently the formation of an insoluble compound due to the action of the electric current cannot occurin the oil or gas strata. As a result, the brine bearing stratum is consolidated or plugged before any appreciable plugging will have occurred in the oil or gas stratum.

Further the method can be used to give improved results over those hitherto attainable, as the ions present in the solution are caused to migrate under the influence of an electric current and as a consequence a greater number of the ions unite producing a larger quantity of precipitate, and thus a more effective seal than when the solutions are separately introduced into the formation and allowed to diffuse and react naturally as inthe conventional manner.

This application is a continuation-in-part of our co-pending application Serial No. 159,330, filed August 16, 1937.

Other modes of applying the principle of our invention may be employed instead of those explained, change being made as regards the method herein disclosed, provided the step or steps stated by any of the following claims or the equivalent or such stated step or steps be employed.

We therefore particularly point out and distinctly claim as our invention:

1. In a method of treating an earth or rock formation the steps which comprise introducing into said formation an aqueous solution containing an ion which will unite with an ion of a solution present 'in said formation to form a relatively insoluble nonmetallic compound, bringing the two solutions into contact with each other and thereafter causing an electric current to pass through the solutions in the formation whereby a non-metallic relatively insoluble precipitate is produced.

2. In a method of treating an earth or rock formation according to claim 1, wherein there is introduced into said formation ahead of the aqueous solution containing a precipitable ion a solution containing ions which will not unite with the ions of either of the other solutions to form a relatively insoluble compound.

3. In a method of treating an earth or rock formation, the steps which comprise introducing separately into said formation two aqueous'solutions, each solution containing an ion which will unite with an ion of the other to form a relatively insoluble compound, and causing an electric cur- Positive ions, such rent to pass through the solutions in said formation, whereby an insoluble deposit is formed byelectrolysis.

4. In a method of treating an earth or rock formation according to claim 3, 'wherein an aqueous solution containing ions that will not unite with the ions of either of the other solutions to form a relatively insoluble compound is introduced into the well between the two solutions containing the precipitable ions.

5. In a method of treating a well, the steps which comprise introducing into the well an aqueous solution containing an ion which will unite with an ion of a brine present in the well to form a relatively insoluble non-metallic compound, and causing an electric current to pass through the solutions in the formation, whereby an insoluble non-metallic deposit is formed by electrolysis.

6. In a method of treating a well according to claim 5, wherein there is introduced into the well ahead of the aqueous solution containing a precipitable ion a solution containing ions which will not unite with the ions of either of the other solutions to form a relatively insoluble compound.

7. In a method of treating a well, the steps which comprise introducing separately into the well two aqueous solutions, each solution containing an ion which will unite with an ion of the other to form a relatively insoluble compound, and causing an electric current to pass through the solutions in the formation, whereby an in-' soluble deposit is formed by electrolysis.

V 8. In a method of treating a well according to claim 7, wherein an aqueous solution containing ions that will not unite with the ions of either of the other solutions to form a relatively insoluble compound is introduced into the well between the two solutions containing the precipitable ions.

, 9. In a method of treating an earth or rock formation penetrated by a well bore, the steps which comprise introducing into the well and thence into the formation an aqueous solution of calciumchloride, thereafter introducing into the well bore an aqueous solution of sodium sulflte, and causing an electric current to pass through the solutions, whereby an insoluble deposit is formed by electrolysis.

JOHN J. GREBE LEONARD C. CHAMBERLAIN. 

